Sorry I can't give you a link or source. But it's real.

I imagine it must be a real marketing challenge. Let me speculate...

Repackaging the product so X% less stock is sold per unit will probably generate an X% increase in sales as people buy more often to replenish it. (Assuming each unit is sold at the same price and consumption remains level). And most people will never notice the difference.

But wait, there's more!

Now add to this the Y%/jar saved by the producer putting less, say, peanut butter, in each jar. Y is smaller than X, the price of the commodity is only a portion of the price of the entire item, a lot of it is packaging, marketing, distribution, overhead, production, etc., but it all adds up. The costs of retooling the factory to produce the new jars (call it Z%/jar) will still yield a profit as long as X+Y > Z.

You will note this holds true even if the price of peanuts and production is constant.

Ah, but what about those savvy consumers that read the label and switch brands when they see the net weight of peanut butter is less? Well, you can estimate with market surveys and so on how many of these will switch to another brand, or quit buying peanut butter altogether, and just factor it in to the equation.

None of this depends on the actual price of peanuts or the costs of bottling them. Another trick is to shape the jar so it carries the same amount of peanut butter, but it is difficult to extract so waste is inevitable. I always suspected this was why ketchup was sold in narrow bottles you could never get completely empty.

During the 70s oil crisis, the price of vinyl recordings skyrocketed because supposedly the LPs and packaging were made of oil products. However, the portion of the cost of the petroleum-derived materials was only a small part of the total cost of each album. Most of it was promotion, advertising, royalties, distribution, etc. I don't recall the exact figures, but a doubling of the price of oil should have resulted in onlyabout a 20% increase in the price per record. Instead, the cost of each album almost doubled...and not one major record company kept prices down to outsell their competitors.